N-heterocyclic carbene (NHC) palladium(II) complexes bearing chiral oxazoline ligands and their catalytic activities in allylic alkylation reactions

Article abstract of DOI:10.3906/kim-1312-60

NHC-Pd(II) complexes bearing a chiral oxazoline ligand (IIIa-f) were synthesized by cleavage of dimeric palladium complexes with the oxazoline ligand. They were fully characterized by ¹H and ¹³C NMR and elemental analyses. The catalytic activity of the complexes (IIIa-f) in allylic alkylation reactions was evaluated. The complex IIIa was found to be the most active catalyst. Very low ee values indicate that the oxazoline is dissociated from the active catalytic species.

Full text of DOI:10.3906/kim-1312-60

Turk J Chem
Turkish Journal of Chemistry
(2014) 38: 679 – 685
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http://journals.tubitak.gov.tr/chem/
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c
⃝ TUBITAK
doi:10.3906/kim-1312-60
Research Article
N-Heterocyclic carbene (NHC) palladium(II) complexes bearing chiral oxazoline
ligands and their catalytic activities in allylic alkylation reactions
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Serpil DENIZALTI , Hayati TURKMEN, Bekir C¸ ETINKAYA
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Department of Chemistry, Ege University, Bornova, Izmir, Turkey
Received: 25.12.2013
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Accepted: 13.02.2014
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Published Online: 15.08.2014
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Printed: 12.09.2014
Abstract: NHC–Pd(II) complexes bearing a chiral oxazoline ligand (IIIa–f) were synthesized by cleavage of dimeric
palladium complexes with the oxazoline ligand. They were fully characterized by 1 H and 13 C NMR and elemental
analyses. The catalytic activity of the complexes (IIIa–f) in allylic alkylation reactions was evaluated. The complex
IIIa was found to be the most active catalyst. Very low ee values indicate that the oxazoline is dissociated from the
active catalytic species.
Key words: N-heterocyclic carbene, oxazoline, palladium complexes, allylic alkylation
1. Introduction
N-Heterocyclic carbenes (NHCs) have emerged as important ligands for transition metals in organometallic
catalysis. In contrast to phosphine complexes, their tight binding to the metal and high temperature, air, and
moisture stability have led to the popularity of these compounds as ligands. The steric and electronic properties
of these ligands can be modified by altering the substituents at the nitrogen atoms and heterocycle. Therefore,
they can be used as ancillary ligands for the preparation of various complexes.1−6 Although palladium NHC
complexes have been successfully developed as highly active precatalysts for C–C coupling reactions (e.g.,
Mizoroki-Heck and Suzuki-Miyaura couplings),7−13 the allylic alkylation reaction using a NHC–Pd has not
been studied extensively. This reaction has proven to be a powerful method for C–C bond forming reactions,
which are synthetically useful. Trost et al. have used the asymmetric allylic alkylation reaction for the total
synthesis of galanthamine, which is utilized in the treatment of Alzhemier’s disease.14 The first example of allylic
alkylation using NHC–Pd complexes was published by Mori and Sato.15,16 In more recent years, enantioselective
versions of allylic alkylation have been reported by several groups.17−26 However, to the best of our knowledge,
allylic alkylation by chiral oxazoline bearing NHC–Pd complexes has not been investigated. To find a more
active catalyst for this reaction and to throw light on the proposed mechanism, herein we report the preparation
of benzimidazol-2-ylidene palladium(II) complexes containing a chiral oxazoline ligand.
2. Results and discussion
2.1. Synthesis and characterization of NHC precursors and NHC–Pd(II) complexes (I–III)
The (5,6-dimethyl)benzimidazolium salts synthesized (almost quantitative yield by quarternization of 1-substituted
(5,6-dimethyl)benzimidazole27 with benzyl bromides) were characterized by 1 H and 13 C NMR spectroscopy.
∗Correspondence: serpil.denizalti@ege.edu.tr
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1 H NMR chemical shifts were consistent with the proposed structures. The resonances for C2 -hydrogens were
observed as sharp singlets between 9.49 and 10.78 ppm. 13 C NMR of these salts showed the C-carbons at
140.4–143.2 ppm. These salts are air- and moisture-stable solids.
The synthesis of dinuclear and monomeric NHC–Pd complexes was carried out according to the literature.28,29
The dinuclear NHC–Pd(II) complexes (IIa–f) were air-stable orange solids slightly soluble in halogenated sol-
vents (Scheme). Dinuclear palladium complexes (IIa–f) and chiral oxazoline were reacted in dichloromethane
to give mixed-NHC–oxazoline complexes of Pd(II) (IIIa–f) as air-stable yellow solids soluble in halogenated
solvents. NMR analyses of the complexes revealed that nitrogen atoms of the chiral oxazoline ligand are coor-
dinated to the palladium center. 13 C NMR spectra of the complexes (IIIa–f) indicated a Ccarbene resonance
between δ 167.1 and 167.3 ppm. The C=N signal in the oxazoline ring was observed between 163.6 and 165.6
ppm.
Scheme. (i) RX, KOH, toluene, EtOH or BuOH; (ii) ArCH2 Br, toluene, reflux; (iii) Pd(OAc)2 , NaBr, DMSO, 90 ◦ C;
(iv) (4S)-4-ethyl-2-phenyl-4,5-dihydro-1,3-oxazole, CH2 Cl2 , 25 ◦ C.
2.2. Allylic alkylation reactions with NHC-Pd(II) complexes (IIIa–f)
NHC-Pd(II) complexes IIIa–f were screened as catalysts for the allylic alkylation reaction of (E)-1,3-diphenyl-
3-en-yl acetate using diethyl malonate as a nucleophile. The catalytic experiments were carried out using 2.5%
mmol palladium complexes IIIa–f as catalysts in the presence of Cs2 CO3 in THF at 50 ◦ C. The results are
summarized in the Figure. The complex IIIa was found to be the most active catalyst (Figure). The activities
of these complexes decreased in the order: IIIa > IIIb > IIIc > IIId > IIIe > IIIf. A comparison of IIIb,
IIIe and IIId, IIIf showed that the methyl groups on the benzimidazole ring decrease the catalytic activity.
The low reaction rate in the complexes with the methylated groups could be explained by the strong α-donating
effect of the NHC ligand, which disfavors the nucleophilic addition step. These observations are consistent with
previous work by Flahaut et al.20 Although the complexes IIIa–f are chiral, very low enantioselectivity was
observed (ee’s up to 3%). This result indicates that the chiral oxazoline ligand leaves the metal center early in
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the catalytic cycle.35,36 Moreover, the development of chiral ligands disconnected to the NHC ligand does not
appear to be promising for chiral induction in the allylic alkylation.
Figure. Allylic alkylation reaction of (E)-1,3-diphenyl-3-en-yl acetate catalyzed by NHC-Pd(II) complexes IIIa–f.
In conclusion, NHC-Pd(II) complexes bearing chiral oxazoline substituents (IIIa–f) were synthesized,
characterized, and used for the allylic alkylation reaction of (E)-1,3-diphenyl-3-en-yl acetate. The complex
IIIa is the most active catalyst. Catalytic activity decreased in the sequence: IIIa > IIIb > IIIc > IIId
> IIIe > IIIf. The results indicated that electron donating groups on the benzene ring of the NHC core or
benzyl substituent decrease the catalytic activity. Unfortunately, no enantioselectivity could be observed. This
behavior seems to be related to the departure of the oxazoline ligand from the metal center early in the catalytic
cycle. Although we failed to achieve asymmetric induction, the yields of the alkylated reaction products are
comparable or even higher than those reported for alternative procedures.19,20
3. Experimental
All manipulations were performed in air unless stated otherwise. All solvents were used as received. 2,4,6-
Trimethylbenzyl bromide, 2,3,5,6-tetramethylbenzyl bromide, and 2,3,4,5,6-pentamethylbenzyl bromide were
synthesized according to methods previously described.30 1-Substituted-(5,6-dimethyl)benzimidazoles and ben-
zimidazolium salts (Ia–Id) were prepared according to a slightly modified procedure from the literature.31−34
All reagents were purchased from Merck, Fluka, Alfa Aesar, and Acros Organics. Melting points were recorded
with a Gallenkamp electrothermal melting point apparatus. FTIR spectra were recorded on a PerkinElmer
Spectrum 100 series spectometer. 1 H NMR and 13 C NMR spectra were recorded with a Varian AS 400 Mer-
cury instrument. Chemical shifts (δ) are given in ppm and coupling constants (J) in Hz. Optical rotations
were taken on a Rudolph Research Analytical Autopol I automatic polarimeter with a wavelength of 589 nm.
The concentration ‘c’ has units of g/100 mL. Elemental analyses were performed on a PerkinElmer PE 2400
elemental analyzer. Quantitative analyses were performed by gas chromatography (Thermo-Finnigan on an
HP-5 capillary column and equipped with a FID detector) at Ege University Faculty of Science.
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3.1. General procedure for the synthesis of 1,3-disubstituted (5,6-dimethyl)benzimidazolium salts
(Ie, f)
1-Methoxyethyl-(5,6-dimethyl)benzimidazole or 1-(2,4,6-trimethyl)benzyl-benzimidazole (5.7 mmol) was dis-
solved in toluene and then 2,4,6-trimethylbenzyl bromide or 2,3,4,5,6-pentamethylbenzyl bromide (5.7 mmol)
was added. The mixture was refluxed for 4 h. The solid that separated out after cooling was filtered off and
washed with diethyl ether (5 mL). The product was recrystallized from CH2 Cl2 /Et2 O.
Ie: Yield 98%. Anal. Calc. C22 H29 BrN2 O: C, 63.25; H, 6.95; N, 6.71. Found: C, 62.98; H, 6.89;
N, 6.67%. mp 210–214 ◦ C. IR: ν˜ = 1565 (ν CN) cm−1
.
1 H NMR (400 MHz, CDCl3): δ = 2.31 (s, 3 H,
CH2 C6 H2 (CH3)3), 2.32 (s, 6 H, CH2 C6 H2 (CH3)3), 2.35 (s, 3 H, CH3 -Ar), 2.42 (s, 3 H, CH3 -Ar), 3.30
(s, 3 H, OCH3), 3.87 (t, J = 4.4 Hz, 2 H, NCH2 CH2 O), 4.83 (t, J = 4.4 Hz, 2 H, NCH2 CH2 O), 5.70 (s,
2 H, CH2 C6 H2 (CH3)3), 6.95 (s, 2 H, CH2 C6H2 (CH3)3), 7.15 (s, 1 H, Ar-H), 7.64 (s, 1 H, Ar-H), 10.24
(s, 1 H, NCH N). 13 C NMR (100 MHz, CDCl3)δ = 20.4 (CH2 C6 H2(C H3)3 -o), 20.8 (CH2 C6 H2(C H3)3 -
p), 20.9 (C H3 -Ar), 21.3 (C H3 -Ar), 46.9 (C H2 C6 H2 (CH3)3), 47.8 (NC H2 CH2 O), 59.1(NCH2C H2 O), 70.1
(OC H3), 113.2, 113.8 (Ar-C -o), 125.2, 129.9 (Ar-C), 130.3 (CH2C6 H2 (CH3)3 -o), 130.9 (CH2C6 H2 (CH3)3 -
m), 137.4 (CH2C6 H2 (CH3)3 -p), 137.5, 138.2 (Ar-C -m), 140.0 (CH2C6 H2 (CH3)3 -o), 141.4 (NC HN).
If: Yield 80%. Anal. Calc. C24 H33 BrN2 O: C, 64.65; H, 7.41; N, 6.29. Found: C, 64.38; H, 7.32;
N, 6.17%. mp 109–110 ◦ C. IR: ν˜ = 1566 (ν CN) cm−1
.
1 H NMR (400 MHz, CDCl3): δ = 2.26 (s, 6
H, CH2 C6 (CH3)5), 2.27 (s, 6 H, CH2 C6 (CH3)5), 2.29 (s, 3 H, CH2 C6 (CH3)5), 2.41 (s, 3 H, CH3 -Ar),
2.45 (s, 3 H, CH3 -Ar), 3.27 (s, 3 H, OCH3), 3.83 (t, J = 4.8 Hz, 2 H, NCH2 CH2 O), 4.87 (t, J = 4.8
Hz, 2 H, NCH2 CH2 O), 5.30 (s, 2 H, CH2 C6 (CH3)5), 7.42 (s, 1 H, Ar-H), 7.72 (s, 1 H, Ar-H), 9.49 (s,
1 H, NCH N). 13 C NMR (100 MHz, CDCl3)δ = 17.1 (CH2 C6(C H3)5 -m), 17.2 (CH2 C6(C H3)5 -o), 17.5
(CH2 C6(C H3)5 -p), 20.8 (C H3 -Ar), 20.9 (C H3 -Ar), 47.5 (CH2 C6(C H3)5 -2,3,4,5,6), 48.0 (NC H2 CH2 O),
59.1 (NCH2C H2 O), 70.3 (OC H3), 112.9, 114.0 (Ar-C -o), 124.9 (Ar-C), 129.9 (CH2C6 (CH3)5), 130.9 (Ar-
C), 133.7 (CH2C6 (CH3)5 -m), 134.2 (CH2C6 (CH3)5 -p), 137.5 (CH2C6 (CH3)5 -o), 137.6, 137.7 (Ar-C -m),
140.4 (NC HN).
3.2. Synthesis of dimeric NHC-Pd(II) complexes (IIa–f)
A mixture of salt (Ia–f) (1.2 mmol), Pd(OAc)2 (1.2 mmol), and NaBr (3.6 mmol) in DMSO was stirred at 90
◦ C for 24 h. The solvent was removed by vacuum distillation. The resulting residue was suspended in CH2 Cl2
and then H2 O was added and the organic phase dried over Na2 SO4 . Concentration of the organic phase and
the addition of Et2 O afforded complexes IIa–f as an orange solid.
3.3. Synthesis of mixed NHC-oxazoline Pd(II) complexes (IIIa–f)
A mixture of dinuclear complex (IIa–f) (0.17 mmol) and (4R)-4-ethyl-2-phenyl-4,5-dihydro-1,3-oxazole was
suspended in CH2 Cl2 (5 mL) and stirred at room temperature for 3 h. After removal of the solvent, complexes
IIIa–f were obtained as yellow solids, which were washed with Et2 O and dried.
IIIa: Yield 45%. Anal. Calc. C38 H43 Br2 N3 OPd: C, 55.39; H, 5.26; N, 5.10. Found: C, 55.32; H, 5.23;
N, 5.07%. mp 119–122 ◦ C. IR: ν˜ = 1643 (ν CN-ox) cm−1 . [α] = –37.50 (c. 0.16, 24.6 ◦ C). 1 H NMR (400
MHz, CDCl3)δ = 1.11 (t, J = 8.0 Hz, 3 H, Ox-CH2 CH3), 2.05–2.12 (m, 1 H, Ox-CH2 CH3), 2.33 (s, 12 H,
CH2 C6 H2 (CH3)3), 2.35 (s, 6 H, CH2 C6 H2 (CH3)3), 2.66–2.72 (m, 1 H, Ox-CH2 CH3), 4.27 (m, 1 H, Ox-
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CH), 4.62–4.69 (m, 2 H, Ox-CH2), 6.19 (s, 4 H, CH2 C6 H2 (CH3)3), 6.18–6.21 (m, 2 H, Ar-H), 6.70–6.73 (m, 2
H, Ar-H), 6.94 (s, 4 H, CH2 C6H2 (CH3)3), 7.39–7.46 (m, 3 H, Ox-Ar-H), 8.82 (d, J = 8.0 Hz, 2 H, Ox-Ar-H).
13 C NMR (100 MHz, CDCl3)δ = 10.0 (Ox-CH2C H3), 21.2 (CH2 C6 H2(C H3)3 -o), 21.3 (CH2 C6 H2(C H3)3 -
p), 28.5 (Ox-CH2C H3), 51.6 (C H2 C6 H2 (CH3)3), 68.2 (Ox-C H), 72.9 (Ox-C H2), 111.3 (Ar-C -o), 122.7 (Ar-
C -m), 126.9 (Ox-Ar-C -p), 127.8 (Ox-Ar-C -m), 128.2 (Ox-Ar-C -o), 129.8 (CH2C6 H2 (CH3)3 -m), 130.5 (Ar-
C), 132.7 (CH2C6 H2 (CH3)3 -p), 135.2 (Ox-Ar-C), 138.9 (CH2C6 H2 (CH3)3 -o), 139.1 (CH2C6 H2 (CH3)3),
166.1 (Ox-C N), 167.3 (Ccarbene).
IIIb: Yield 40%. Anal. Calc. C31 H37 Br2 N3 O2 Pd: C, 49.65; H, 4.97; N, 5.60. Found: C, 49.59;
H, 4.94; N, 5.59%. mp 173–177 ◦ C. IR: ν˜ = 1644 (ν CN-ox) cm−1 . [α] = –31.21 (c. 0.26, 26.6 ◦ C). 1 H
NMR (400 MHz, CDCl3)δ = 1.10 (t, J = 7.6 Hz, 3 H, Ox-CH2 CH3), 2.06–2.13 (m, 1 H, Ox-CH2 CH3),
2.32 (s, 6 H, CH2 C6 H2 (CH3)3), 2.36 (s, 3 H, CH2 C6 H2 (CH3)3), 2.66–2.73 (m, 1 H, Ox-CH2 CH3), 3.35
(s, 3 H, OCH3), 4.15 (t, J = 6.0 Hz, 2 H, NCH2 CH2 O), 4.27 (t, J = 6.4 Hz, 1 H, Ox-CH), 4.62–4.68
(m, 2 H, Ox-CH2), 5.02 (t, J = 6.0 Hz, 2 H, NCH2 CH2 O), 6.12 (s, 2 H, CH2 C6 H2 (CH3)3), 6.15 (d,
J = 8.0 Hz, 1 H, Ar-H), 6.85 (t, J = 8.0 Hz, 1 H, Ar-H), 6.96 (s, 2 H, CH2 C6H2 (CH3)3), 7.10 (t,
J = 8.0 Hz, 1 H, Ar-H), 7.45–7.55 (m, 4 H, Ox-Ar-H , Ar-H ), 8.76 (d, J = 7.6 Hz, 2 H, Ox-Ar-H).
13 C NMR (100 MHz, CDCl3)δ = 10.1 (Ox-CH2C H3), 21.1 (CH2 C6 H2(C H3)3 -o), 21.3 (CH2 C6 H2(C H3)3 -
p), 28.5 (Ox-CH2C H3), 48.8 (NC H2 CH2 O), 51.4 (C H2 C6 H2 (CH3)3), 59.4 (OC H3), 68.3 (Ox-C H), 71.5
(NCH2C H2 O), 72.9 (Ox-C H2), 111.2, 111.4 (Ar-C -o), 122.8, 123.2 (Ar-C -m), 126.8 (CH2C6 H2 (CH3)3 -m),
127.6 (Ox-Ar-C -o), 128.3 (Ox-Ar-C -m), 129.8 (Ox-Ar-C -p), 130.4, 132.7 (Ar-C), 134.7 (CH2C6 H2 (CH3)3 -p),
135.9 (Ox-Ar-C), 139.1 (CH2C6 H2 (CH3)3 -o), 139.3 (CH2C6 H2 (CH3)3), 165.6 (Ox-C N), 167.3 (Ccarbene).
IIIc: Yield 56%. Anal. Calc. C32 H39 Br2 N3 O2 Pd: 50.31; H, 5.15; N, 5.50. Found: C, 50.25; H, 5.11;
N, 5.48%. mp 192–195 ◦ C. IR: ν˜ = 1642 (ν CN-ox) cm−1 . [α] = –35.81 (c. 0.25, 26.9 ◦ C). 1 H NMR (400
MHz, CDCl3)δ = 1.12 (t, J = 7.2 Hz, 3 H, Ox-CH2 CH3), 2.07–2.14 (m, 1 H, Ox-CH2 CH3), 2.26 (s, 3 H,
CH2 C6 H(CH3)4), 2.29 (s, 3 H, CH2 C6 H(CH3)4), 2.69–2.74 (m, 1 H, Ox-CH2 CH3), 3.35 (s, 3 H, OCH3),
4.16 (t, J = 5.6 Hz, 2 H, NCH2 CH2 O), 4.27 (t, J = 6.4 Hz, 1 H, Ox-CH), 4.62–4.69 (m, 2 H, Ox-CH2),
5.03 (t, J = 5.6 Hz, 2 H, NCH2 CH2 O), 6.01 (d, J = 8.0 Hz, 1 H, Ar-H), 6.22 (s, 2 H, CH2 C6 H(CH3)4),
6.81 (t, J = 8.0 Hz, 1 H, Ar-H), 7.09 (t, J = 8.0 Hz, 1 H, Ar-H), 7.12 (s, 1 H, CH2 C6H (CH3)4), 7.44–7.56
(m, 4 H, Ox-Ar-H , Ar-H), 8.78 (d, J = 7.2 Hz, 2 H, Ox-Ar-H). 13 C NMR (100 MHz, CDCl3)δ = 10.1 (Ox-
CH2C H3), 16.8 (CH2 C6 H(C H3)4 -o), 20.7 (CH2 C6 H(C H3)4 -m), 28.5 (Ox-CH2C H3), 48.8 (NC H2 CH2 O),
52.4 (C H2 C6 H(CH3)4), 59.4 (OC H3), 68.3 (Ox-C H), 71.5 (NCH2C H2 O), 72.9 (Ox-C H2), 111.2, 111.6
(Ar-C -o), 122.6, 123.1 (Ar-C -m), 126.8 (CH2C6 H(CH3)4 -p), 128.3 (Ox-Ar-C -o), 130.4 (Ox-Ar-C -m), 130.5
(Ox-Ar-C -p), 132.7 (CH2C6 H(CH3)4 -o), 132.9 CH2C6 H(CH3)4 -m), 134.6, 134.9 (Ar-C), 135.6 (Ox-Ar-C),
135.9 (CH2C6 H(CH3)4), 165.6 (Ox-C N), 167.2 (Ccarbene).
IIId: Yield 78%. Anal. Calc. C33 H41 Br2 N3 O2 Pd: C, 50.95; H, 5.31; N, 5.40. Found: C, 50.86;
H, 5.29; N, 5.36%. mp 199–201 ◦ C. IR: ν˜ = 1639 (ν CN-ox) cm−1 . [α] = –38.46 (c. 0.26, 26.8 ◦ C). 1 H
NMR (400 MHz, CDCl3)δ = 1.11 (t, J = 7.2 Hz, 3 H, Ox-CH2 CH3), 2.09–2.14 (m, 1 H, Ox-CH2 CH3),
2.27 (s, 6 H, CH2 C6 (CH3)5), 2.31 (s, 6 H, CH2 C6 (CH3)5), 2.34 (s, 3 H, CH2 C6 (CH3)5), 2.68–2.73 (m, 1
H, Ox-CH2 CH3), 3.36 (s, 3 H, OCH3), 4.16 (t, J = 6.0 Hz, 2 H, NCH2 CH2 O), 4.29 (t, J = 6.8 Hz, 1 H,
Ox-CH), 4.63–4.68 (m, 2 H, Ox-CH2), 5.03 (t, J = 6.0 Hz, 2 H, NCH2 CH2 O), 6.06 (d, J = 7.2 Hz, 1 H,
Ar-H), 6.23 (s, 2 H, CH2 C6 (CH3)5), 6.79 (t, J = 7.2 Hz, 1 H, Ar-H), 7.08 (t, J = 7.2 Hz, 1 H, Ar-H),
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7.44–7.55 (m, 4 H, Ox-Ar-H , Ar-H), 8.79 (d, J = 7.2 Hz, 2 H, Ox-Ar-H). 13 C NMR (100 MHz, CDCl3)δ =
10.1 (Ox-CH2C H3), 17.1 (CH2 C6(C H3)5 -o), 17.5 (CH2 C6(C H3)5 -p), 17.8 (CH2 C6(C H3)5 -m), 28.5 (Ox-
CH2C H3), 48.7 (NC H2 CH2 O), 52.9 (C H2 C6 (CH3)5), 59.4 (OC H3), 68.3 (Ox-C H), 71.4 (NCH2C H2 O),
72.9 (Ox-C H2), 111.1, 111.7 (Ar-C -o), 122.6, 123.1 (Ar-C -m), 126.8 (Ox-Ar-C -o), 127.9 (Ox-Ar-C -m), 128.3
(Ox-Ar-C -p), 130.4 (CH2C6 (CH3)5 -m), 132.7 (CH2C6 (CH3)5 -o), 133.4 (CH2C6 (CH3)5 -p), 134.9, 135.1 (Ar-
C), 135.9 (Ox-Ar-C), 136.5 (CH2C6 (CH3)5), 165.5 (Ox-C N), 167.2 (Ccarbene).
IIIe: Yield 79%. Anal. Calc. C33 H41 Br2 N3 O2 Pd: C, 50.95; H, 5.31; N, 5.40. Found: C, 50.91; H,
5.28; N, 5.41%. mp 174–176 ◦ C. IR: ν˜ = 1639 (ν CN-ox) cm−1 . [α] = –9.17 (c. 0.11, 28.2 ◦ C). 1 H NMR
(400 MHz, CDCl3)δ = 1.14 (t, J = 7.6 Hz, 3 H, Ox-CH2 CH3), 2.01 (s, 3 H, CH2 C6 H2 (CH3)3), 2.09–2.14
(m, 1 H, Ox-CH2 CH3), 2.26 (s, 6 H, CH2 C6 H2 (CH3)3), 2.33 (s, 3 H, CH3 -Ar), 2.38 (s, 3 H, CH3 -Ar),
2.65–2.71 (m, 1 H, Ox-CH2 CH3), 3.35 (s, 3 H, OCH3), 4.13 (t, J = 6.4 Hz, 2 H, CH2), 4.28 (t, J = 6.8 Hz,
1 H, Ox-CH), 4.62–4.70 (m, 2 H, Ox-CH2), 4.94 (t, J = 6.4 Hz, 2 H, CH2), 5.85 (s, 1 H, Ar-H), 6.04 (s, 2
H, CH2 C6 H2 (CH3)3), 6.95 (s, 2 H, CH2 C6H2 (CH3)3), 7.19 (s, 1 H, Ar-H), 7.47–7.55 (m, 3 H, Ox-Ar-H),
8.77 (d, J = 8.0 Hz, 2 H, Ox-Ar-H). 13 C NMR (100 MHz, CDCl3)δ = 10.1 (Ox-CH2C H3), 20.3, 20.6 (Ar-
C H3), 21.1 (CH2 C6 H2(C H3)3 -o), 21.3 (CH2 C6 H2(C H3)3 -p), 28.4 (Ox-CH2C H3), 48.5 (NC H2 CH2 O),
51.1 (C H2 C6 H2 (CH3)3), 59.4 (OC H3), 68.2 (Ox-C H), 71.5 (NCH2C H2 O), 72.7 (Ox-C H2), 111.3, 111.9
(Ar-C -o), 126.9 (CH2C6 H2 (CH3)3 -m), 127.9 (Ox-Ar-C -o), 128.2 (Ox-Ar-C -m), 129.5 (Ox-Ar-C -p), 130.4
(Ar-C), 131.6, 132.5 (Ar-C -m), 133.3 (CH2C6 H2 (CH3)3 -p), 134.5 (Ox-Ar-C), 138.7 (CH2C6 H2 (CH3)3 -o),
139.4 (CH2C6 H2 (CH3)3), 163.7 (Ox-C N), 167.1 (Ccarbene).
IIIf: Yield 77%. Anal. Calc. C35 H45 Br2 N3 O2 Pd: C, 52.16; H, 5.63; N, 5.21. Found: C, 52.13; H,
5.61; N, 5.20%. mp 162–165 ◦ C. IR: ν˜ = 1640 (ν CN-ox) cm−1 . [α] = –8.77 (c. 0.11, 26.8 ◦ C). 1 H NMR (400
MHz, CDCl3)δ= 1.14 (t, J = 7.6 Hz, 3 H, Ox-CH2 CH3), 1.96 (s, 3 H, CH2 C6 (CH3)5), 2.08–2.16 (m, 1 H,
Ox-CH2 CH3), 2.21 (s, 3 H, CH3 -Ar), 2.29 (s, 6 H, CH2 C6 (CH3)5), 2.32 (s, 6 H, CH2 C6 (CH3)5), 2.38 (s, 3
H, CH3 -Ar), 2.68–2.74 (m, 1 H, Ox-CH2 CH3), 3.37 (s, 3 H, OCH3), 4.14 (t, J = 5.6 Hz, 2 H, CH2), 4.28 (t, J
= 6.8 Hz, 1 H, Ox-CH), 4.63–4.70 (m, 2 H, Ox-CH2), 4.94 (t, J = 5.6 Hz, 2 H, CH2), 5.76 (s, 1 H, Ar-H), 6.14
(s, 2 H, CH2 C6 (CH3)5), 7.18 (s, 1 H, Ar-H), 7.47–7.55 (m, 3 H, Ox-Ar-H), 8.79 (d, J = 7.2 Hz, 2 H, Ox-Ar-
H). 13 C NMR (100 MHz, CDCl3)δ = 10.1 (Ox-CH2C H3), 17.1 (CH2 C6(C H3)3 -o), 17.5 (CH2 C6(C H3)3 -p),
17.9 (CH2 C6(C H3)3 -m), 20.3 (Ar-C H3), 20.6 (Ar-C H3), 28.4 (Ox-CH2C H3), 48.5 (NC H2 CH2 O), 52.6
(C H2 C6 (CH3)5), 59.4 (OC H3), 68.3 (Ox-C H), 71.4 (NCH2C H2 O), 72.7 (Ox-C H2), 111.2, 112.3 (Ar-C -o),
126.9 (Ox-Ar-C -p), 128.2 (Ox-Ar-C -m), 130.4 (Ox-Ar-C -o), 131.3, 131.4 (Ar-C), 132.6 (CH2C6 (CH3)5 -p),
133.0, 133.5 (Ar-C -m), 134.6 (CH2C6 (CH3)5 -o), 135.2 (Ox-Ar-C), 136.1 (CH2C6 (CH3)5), 163.6 (Ox-C N),
167.1 (Ccarbene).
Acknowledgments
¨
¨ ˙
We thank Ege University Research Fund (2009/Fen/029) and TUBA for financial support and TUBITAK for a
grant.
References
1. D´ıez-Gonza´lez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612–3676.
2. Hahn, F. E.; Jahnke, M. C. Angew. Chem. Int. Ed. 2008, 47, 3122–3172.
684

˙
DENIZALTI et al./Turk J Chem
3. Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G. Angew. Chem. Int. Ed. 2007, 46, 2768–2813.
4. D´ıez-Gonza´lez, S.; Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874–883.
5. Herrmann, W. A. Angew. Chem. Int. Ed. 2002, 41, 1290–1309.
6. Herrmann, W. A. Angew. Chem. Int. Ed. Engl. 1997, 36, 2162–2187.
7. Tu¨rkmen, H.; Pelit, L.; C¸etinkaya, B. J. Mol. Cat. A: Chemical 2011, 1–2, 88–93.
8. Marion, N.; Nolan, S. P. Acc. Chem. Res. 2008, 41, 1440–1449.
¨
9. Ozdemir, I.; Arslan, H.; Demir, S.; VanDerveer, D.; C¸etinkaya, B. Inorg. Chem. Commun. 2008, 12, 1462–146.
˙
¨
10. Ozdemir, I.; Yigit, M.; C¸etinkaya, E.; C¸etinkaya, B. Appl. Organometal. Chem. 2006, 20, 87–192.
˙
11. O’Brien, C. J.; Kantchev, E. A. B.; Valente, C.; Hadei, N.; Chass, G. A.; Lough, A.; Hopkinson, A. C.; Organ, M.
G. Chem. Eur. J. 2006, 12, 4743–4748.
12. Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. Angew. Chem. Int. Ed. 2003, 43, 3690–3693.
13. Magill, A. M.; McGuinness, D. S.; Cavell, K. J.; Britovsek, G. J. P.; Gibson, V. C.; White, A. J. P.; Williams, D.
J.; White, A. H.; Skelton, B. W. J. Organomet. Chem. 2001, 617–618, 546–560.
14. Trost, B. M.; Tang, W.; Toste, F. D. J. Am. Chem. Soc. 2006, 127, 14785–14803.
15. Sato, Y.; Yoshino, T.; Mori, M. Org. Lett. 2005, 5, 31–33.
16. Sato, Y.; Mori, M. J. Organomet. Chem. 2003, 690, 5753–5758.
17. Shirasaki, H.; Kawakami, M.; Yamada, H.; Arakawa, R.; Sakaguchi, S. J. Organomet. Chem. 2013, 726, 46–55.
18. Toselli, N.; Martin, D.; Buono, G. Org. Lett. 2008, 10, 1453–1456.
19. Zhang, T.; Shi, M.; Zhao, M. Tetrahedron 2008, 64, 2412–2418.
20. Flahaut, A.; Roland, S.; Mangeney, P. Tetrahedron: Asymmetry 2007, 18, 229–236.
´
21. Roseblade, S. J.; Ros, A.; Monge, D.; Alcarazo, M.; Alvarez, E.; Lassaletta, J. M.; Ferna´ndez, R. Organometallics
2007, 26, 2570–2578.
22. Merzouk, M.; Moore, T.; Williams, N. A. Tetrahedron Lett. 2007, 48, 8914–8917.
23. Li, S. J.; Zhong, J. H.; Wang, Y. G. Tetrahedron: Asymmetry 2006, 17, 1650–1654.
´
24. Ros, A.; Monge, D.; Alcarazo, M.; Alvarez, E.; Lassaletta, J. M.; Ferna´ndez, R. Organometallics 2006, 25, 6039–
6046.
25. Hodgson, R.; Douthwaite, R. E. J. Organomet. Chem. 2005, 690, 5822–5831.
26. Bonnet, L. G.; Douthwaite, R. E. Organometallics 2003, 22, 4187–4189.
27. Denizaltı, S. MSc, Ege University, 2006.
28. Han, Y.; Huynh, H. V.; Tan, G. K. Organometallics 2007, 26, 6447.
29. Tu¨rkmen, H.; Pape, T.; Hahn, F. E.; C¸etinkaya, B. Eur. J. Inorg. Chem. 2009, 285–294.
30. Van der Made, A. W.; Van der Made, R. H. J. Org. Cem. 1993, 58, 1262–1263.
¨
31. Ozdemir, I.; S¸ahin, N.; G¨ok, Y.; Demir, S.; C¸etinkaya, B. J. Mol. Cat. A: Chemical 2005, 234, 181–185.
˙
¨
˙
32. Ozdemir, I.; C¸etinkaya, E.; C¸etinkaya, B.; C¸i¸cek, M.; S´emeril, D.; Bruneau, C.; Dixneuf, P. H. Eur. J. Inorg. Chem.
2004, 418–422.
¨
˙
¨
˙
¨
33. Ozdemir, I.; Demir, S.; Gu¨nal, S.; Ozdemir, I.; Arıcı, C.; Ulku¨, D. Inorg. Chim. Acta 2010, 363, 3803–3808.
¨
34. Gu¨rbu¨z, N.; Ya¸sar, S.; Ozcan, E. O.; Ozdemir, I.; C¸etinkaya, B. Eur. J. Inorg. Chem. 2010, 3051–3056.
¨
¨
˙
35. Canseco-Gonzalez, D.; Gniewek, A.; Szulmanowicz, M.; Mueller-Bunz, H.; Trzeciak, A. M.; Albrecht, M. Chem.
Eur. J. 2012, 18, 6055–6062.
36. Canseco-Gonzalez, D.; Petronilho, A.; Mueller-Bunz, H.; Ohmatsu, K.; Ooi, T.; Albrecht, M. J. Am. Chem. Soc.
2013, 135, 13193–13203.
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